There are various needs for a door which prevents reversal of air flow direction when an exhaust fan fails. Usually these types of doors are pivoted about an upper portion of a frame of an exhaust fan support system at the exhaust area and the rushing air pushes the door open and escapes. Whenever the exhaust fan stops, the air flow ceases and the door, under the force of gravity, closes against the exhaust duct of the exhaust fan and provides a seal, with some minimal leakage, which prevents air from rushing in the reverse direction into the exhaust fan area.
Exhaust fans are used for ventilation of underground mines. Each of the ventilation fans ventilate and exhaust air from the underground mine by pulling a draft of air through the exhaust fan and out to the atmosphere at the surface. If an exhaust fan fails, it is important that air does not flow from the atmosphere back into the mine through the ventilation fan. To prevent that, an air flow reversal prevention door is mounted at the exhaust of a ventilation or exhaust fan. The door is held open by the force of air when the fan is operating and when the fan stops the air flow ceases and the door collapses by gravitational pull against the ventilation fan exhaust and remains in a vertical position where it seals (with some minimal leakage) and prevents air from reversing its direction from the atmosphere to enter the exhaust system. Compliance with mining regulations requires that air reversal doors on all ventilation fans for underground mines must be tested frequently, usually every thirty days, to determine that they close properly. It is possible that a fan door, once it is held open by the force of the air exhausting from the ventilation fan, could be held open by some malfunction of the structure which supports 10 the fan door to enable it to pivot about a top portion of the ventilation fan structure which would prevent the fan door from dropping into its vertical position to seal against air flow entering the ventilation fan area after the ventilation fan ceases to function.
To test the functioning of the air flow reversal prevention door requires that the ventilation fan be shut off to insure that the door collapses. While the test is being performed, no one is permitted underground and all personnel must be evacuated from the mine. Shutting off the fan adversely affects the fan motor and in time will cause motor failure. Also, shutting down one fan in a multiple fan mine may cause problems to one of the other fans in the mine. If the fan is not restarted within 15 minutes of shut off time, power to the mine must be interrupted.
The purpose for determining that air flow reversal doors close properly when a fan fails is to ensure the safety of the people in the mine at the time at the time of failure. If the air flow reversal prevention door fails to close properly when the fan fails or is shut off, vacuum pressure caused by the other mine fans which are still operating will cause methane contaminated air to be pulled out of the return area of the mine into the active portions of the mine where a methane buildup or explosion can occur.
There is no known method which provides a means for testing the proper function of the reversal prevention door while the ventilation fan is in operation. The present invention solves the problem by providing a structure with the air flow reversal prevention door which permits testing of the movement of the door and operation of a seal with the door while the ventilation fan is in operation.